When machining a workpiece using an automated multi-axis machining tool, such as a computer numerical control (CNC) machine tool, it is necessary to keep the workpiece fixed relative to a reference point so that the workpiece can be cut, milled, or otherwise formed with accuracy. If the workpiece is not fixed relative to a reference point during the machining process, the resulting product will likely be formed outside of specifications, and the CNC machine tool may be subject to an increased risk of crashing, which could result in damage to the cutting tool and other components of the tool.
In order to fix the position of the workpiece relative to a reference point during the machine process, it is common to mount the workpiece to a prior art workpiece holder. Prior to mounting a workpiece to an existing workpiece holder, a pair of dovetail grooves are typically machined in opposite external edges of a bottom portion of the workpiece. The dovetail grooves provide a pair of opposing surfaces that form a single male protrusion on the workpiece that allow the workpiece holder to grip the workpiece along the x and y axes using a pair of opposing clamping members. The clamping members can either be mechanically actuated to move toward one another to grip the dovetail grooves, or one of the clamping members may be fixed in a stationary position while the other clamping member is moved toward the stationary clamping member to grip the dovetail grooves. After the workpiece is formed by the CNC machining tool, the dovetail grooves (i.e., the single male protrusion) are machined off.
While existing workpiece holders are capable of maintaining the workpiece in a fixed position along the x and y axes relative to a reference point, they suffer from a number of drawbacks and deficiencies that introduce a number of inefficiencies into the machining process. For example, existing workpiece holders may include a spring that is used to bias one of the clamp members in a direction that assists in disengaging the clamp member from the dovetail groove. However, the moveable clamp member is susceptible to binding within the body of the workpiece holder when disengaging from the dovetail groove due to the forces imposed by the moment arm created between the clamp screw and the actual clamp contact area of the workpiece and associated distance away. This offset distance or moment arm may cause a bind that the spring cannot overcome. When the workpiece cannot be easily released from the workpiece holder, this causes delays in manufacturing the workpiece. Further inefficiencies are present at the beginning of the machining process due to the need to machine two separate dovetail grooves in opposite external edges of the bottom portion of the workpiece, and also after the machining process is complete when the entire bottom surface of the workpiece needs to be machined off to remove the dovetail grooves. Additionally, even though the workpiece holder operates to restrict the movement of the workpiece along the x and y axes, one or more separate indexing features are also typically included to properly orient the workpiece to the workpiece holder and prevent movement of the workpiece along the z axis, which is perpendicular to both the x and y axes. However, using the indexing feature to properly position the workpiece introduces an additional step and a further inefficiency in the machining process. Furthermore, the prior art has limitations to the clamping forces it may apply on the workpiece due to only clamping in one direction and using a indexing feature in the other.
As such, there is a need for a workpiece holder that is not susceptible to binding when releasing a workpiece from the workpiece holder. There is also a need to reduce the amount of machining that needs to be done on a workpiece in order for the workpiece to be mounted to the workpiece holder. There is a further need for a workpiece holder with a clamping mechanism that restricts movement of workpiece along the x, y and z axes without the need for a separate indexing feature. The present invention addresses these and other needs, such as the benefit of higher clamping forces in multiple directions.